Vibration detector



April 21, 1936. o. E. DUDLEY 2,038,101

VIBRATION DETECTOR Filed Feb. 18, 1931 2 Sheets-Sheet 1 3i, 2s- /2 25 32 z l5 [6 /5 i l4 LE:

44 40 4511/ WM 2/ 22 /a I lNVENTOR dam/e5 fluomr BY ATTORNEY WJ fl Apyifl 2i, 3. Q DUDLEY 2,038,101

' VIBRATION DETECTOR Fiied Feb. 18, 1951 2 Sheets-Sheet 2 INVENTOR Oscme 50004:)"

BY ATTORNEY Ky i Patented Apr. 21, 1936 UNITED STATES VIBRATION DETECTOR Oscar E. Dudley, Houston, Tex., assignor to The Texas Company, New York, N. Y., a corporation of Delaware Application February18, 1931,, Serial No. 516,675

2 Claims. (Cl. 177-352} This invention relates to vibration detectors, more particularly to devices for detecting sound or similar compressional waves coming through the air or through some'solid medium, such as the earth.

Heretafore the majority of detectors designed for the above purpose have involvd'some sort of magneto electric constructions, i. e., one in which a variation of magnetic flux cutting across a coil or similar conductor is made to induce a current therein in response to a vibration. Detectors of this type have involved a relatively complicated construction and have been dificult to maintain in adjustment. Furthermore the currents induced by virtue of the sound or other compressional waves striking the detector have frequently been very feeble and have necessitated the use of cumbersome and expensive amplifying apparatus before being transmitted to a suitable indicating or recording device, such as a galvanometer or oscillograph.

A primary object of my invention has been to devise a suitable detector which is compact, relatively simple of construction and operation and readily adjustable. To this end the present invention contemplatesthe use of a sensitive and compact microphone, and structure for directing against the microphone small pads of air generated in response to the reception of compressional waves. The microphone is to be connected in any suitable circuit which will give an indicav tion of the changes in resistance of the microphone corresponding to the received compressional waves.

For a. better understanding 10! the invention reference may be had to the accompanying dedetector as being housed in a casing formed of I a lower or base portion l0 and an upper or cover portion I I. This casing is adapted tobe inserted or buried in the earth so as to make good contact therewith, in order that compressional wave vibrations, passing through the earth will cause the casing to vibrate in accordance with the duration and amplitude of the waves. The upper or cover portion H is adapted to be secured to the lower portion in by suitable means, such as the screws I2. An annular flange I3 is formed preferably integral with the lower surface of the casing portion H and a groove l4 formed in the upper surface of the casing portion l0 receives the projection I3. The groove I4 contains suitable packing l5 and thus, it will be seen that as the bolts 52 are tightened, a tight and moisture proof joint is obtained between the two casing portions. r

An annular supporting ring I6 is threaded into the upper inner edge of the casing portion Hi, this ring It serving-to support the remaining parts of the detector. A plurality of legs H are rigidly secured to the lower surface of the supporting ring it and in turn serve to support a base member or wave responsive element 38. A clamping ring is is mounted between the base member It and the legs H and serves to hold the ends of a corrugated cross 20 preferably formed of leather, or some similar material. The purpose of this cross will be explained hereinafter. The wave responsive element or base member I8 is provided with a groove 25 which serves to hold a quantity of a'liquid 22, such as mercury.

To the upper surface of the supporting ring it is rigidly secured a plurality of legs 23 similar to the legs H, the legs 23 acting as a support for. a

pair of clamping rings 24 between which is se cured the ends of a second corrugated cross 25 similar to the cross 20. A third set of supporting legs 26 are adapted to be secured to. the legs 23 and hold the clamping rings 24 and the cross 25 firmly in position. A pair of screws 21 are attached to the upper endsoi' two of the legs 26 and supporta bar 28 of some suitable insulating material, such as a phenol condensation product. As will be seen with reference to Fig. 1, the bar 28 is adjustably mounted on the screws 21-so that it may be raised or loweredas desired.

The inertia element 29 shown in face view in Fig. 3 is yieldably suspended from a helical spring 30 which in turn is adjustably secured to the center of the bar 28 by means of a screw 3|. The inertia element 29 comprises essentially a supporting disc 32 at the center of which is secured a suitable microphone 33 and a. spacer ring 34 mounted at the edge of the disc 32. To this spacer ring is attached a diaphragm clamping member 35 by means of' suitable screws 36. A corrugated diaphragm 31 is clamped between the spacer ring 34 and the member 35 and at the center of the diaphragm 31 is attached a small bolt 38 which is secured to the movable member, not shown, of the microphone. A pair of spacing clamps 39 are attached to the upper surface of the spacer ring 34 and serve both as a means for attaching the lower end of the spring and as a means for clamping the middle portion oi the upper corrugated cross 25. The purpose. oi the cross is to yieldably maintain the inertia element in mid position relative to the supporting ring I6. I To the lower surface of thespacer ring 22 secured a bell shaped member 40 by means oi. a pair of screws 4i passing through a spacer 42.

The mid portion or the lower corrugated cross 2! is clamped between the spacer l2 and the bell member 40, thus yieldably' maintaining the lower portion of the inertia element also in mid position with respect to the supporting ring Ii. It is to be understood that in place of the corrugated crosses 20 and 25, a pair of relatively soft, leather diaphragms may also be used. Thebell member 40 is provided with a depending flange 43 which is normallypartially immersed in the'liquid 22. An air chamber 44 is thus formed between the bell 40 and the base or wave responsive element IS, the liquid 22 serving as a seal for the outer portion 01' the-air chamber. The air chamber 44 is provided with an outletduct 45 at the upper end of which is mounted a conduit 48 which leads through the diaphragm clamping member 35 to be secured to such binding posts. An opening ll is provided in the center of the upper casing portion II, this opening serving to allow the passage of a small tool, such as a wrench, to, be used in adjusting the position of the screw II and the tension of the spring 20.

In the operation of the detector, sound or other compressional waves passing 'through'the ea will cause the casing, and consequently the pporting ring I6 and the wave responsive element 18 to vibrate in synchronism with the waves;

The inertia element 29 being yieldably supported from the spring will remain substantially stationary and it will be seen that the size or the air chamber I! will vary in accordance with the relative movement between the bell 4! and the wave responsive element or base member ll caused by the vibration oi the wave responsive s,oae,1o1 A element by the compressional waves. As the volume of the air chamber 44 fluctuates, puiis of air will pass through the outlet 45 and conduit ll and will impinge on the microphone diaphragm 21. The electrical resistance of the microphone will consequently vary in response to these pufls of air and suitable apparatus, which may be attached to the microphone leads, will serve to indicate or record these variations in resistance and thus the amplitude and duration of the compressional wave vibrations.

While I have described my invention as embodied in concrete form and operating in a speciflc manner in accordance with the provisions of the patent sta utes, it should be understood that I do not limit my invention thereto, since various'modiflcations thereof will suggest themselves to those skilled in the art without departing from the spirit of my invention,-the scope of which is set forth in the annexed claims.

I claim: I

1. In a device or the class described, a housing responsive to compressional wave vibrations, a supporting base rigidly secured to and within said housing, an inertia member resiliently supported from said housing, a portion of said inertia member including an" air chamber, 9. diaphragm closing one side of said air chamber, a

- microphone connected so as to be actuated by movement of said diaphragm, means including said supporting base and said inertia member forming a second expansible air chamber, and a conduit connecting said second air chamber with the air chamber in said inertia element, the arrangement being such that the output of said conduit caused by fluctuations in the volume of said second air chamber will be delivered within said first mentioned chamber against said diaphragm so; that said diaphragm will be vibrated in accordance with said fluctuations.

.2. In a detector, a casing responsive to compresslonal wave vibrations, a supporting ring mounted in said casing, a base member rigidly secured to said ring, an inertia element yieldably suspended from said ring, means including said inertia element and said base member iorming" an expansible air chamber, a microphone moimted on said inertia element, a diaphragm connect-- ed to said microph one, a member forming with said diaphragm a second enclosed chamber, and a conduit leading from said first mentioned chamber, the'other end of said conduit opening into said second chamber so that fluctuations in the volume of said flrst mentioned chamber will cause pu'fls of air to pass through said conduit into said secondchaniber to actuate said diaphragm and said microphone.

v OSCAR E. DUDLEY. 

